Hawaiian Electric Co. is urging customers to hang on tight to metallic balloons and other celebration materials, after metallic streamers caused an outage early this morning.

Metallic streamers released from an air cannon onto power lines knocked out the power for 300 customers in the Keeaumoku area today from 1 a.m. to 3 a.m.

The electric utility sent out an announcement after the incident, asking residents to refrain from letting go of metallic balloons or streamers near power lines because the materials can cause a short circuit. HECO said last year metallic balloons caught in power lines resulted in 30 outages, causing 42,161 customers to lose power.

“We can’t control the weather, but outages caused by metallic balloons and streamers are preventable,” said Shannon Tangonan, HECO spokeswoman. “We just ask that people take the extra step to secure these balloons by adding a weight to the end of the string or ribbon. Releasing these balloons, whether intentional or not, can knock out power to hundreds, if not thousands of customers.”

HECO said outages caused by balloons spike during graduation season in May and June.